A custom Maven Mojo to show the effective project properties

A custom Maven Mojo?!

Recently I came across the requirement to print all effective project properties during a Maven build. So, why not write a custom Mojo to do that?

I try to get more into writing custom Maven Mojos, so I created a new project and put together a simple class that accesses the current project and prints all project properties to the Maven build log in info level.

If you are interested in the code, you can head over to my GitHub and check it out: https://github.com/NilsCoding/mvn-show-settings

What I've learned in this project

Injecting the Maven project

You can annotate a field of type org.apache.maven.project.MavenProject with the @Parameter annotation and specify defaultValue = "${project}" as an annotation attribute to inject the current project as an object into the Mojo.

Dependency for MavenProject inject

Also, you need to add org.apache.maven:maven-core as a dependency to have access to MavenProject.

I've included more Maven dependencies in my mvn-show-settings project (and commented out some injects in the Mojo code) to have a starting point for extending the Mojo by using more information at build time.

Custom configuration for helper class generation

A custom Maven Mojo project needs some configuration files and a helper class, so it is highly recommeded to include org.apache.maven.plugins:maven-plugin-plugin in the build process to auto-generate those files. As a side-note, you might want to configure helpPackageName for that plugin to specify the package of the generated helper class. Otherwise, a package name will be generated from the artifact name and will result in a (maybe) unwanted package name.

Excluding generated code from Checkstyle

I've also added a custom Checkstyle configuration to my project to enforce some coding "standards". By default, all sources will be checked, which also includes the gerenated sources for the helper classes. To prevent those helper classes from being checked, you can specify which directories should be included by the Checkstyle plugin:

<sourceDirectories>
    <sourceDirectory>${project.build.sourceDirectory}</sourceDirectory>
</sourceDirectories>

If you configure Checkstyle to be used in the reporting, then you might want to add this configuration there, too.

What's next?

I'm currently working on some other custom Maven Mojos which I will definitely publish on GitHub, too, and there will also be some interesting details on what you can actually do in custom Maven Mojos.

So, stay tuned. 😉